Commercial nanofabrication is currently limited by available technologies. Few allow manipulation in the nanometer range. The spatially selective deposition according to the present invention may be for the purpose of manufacture of solid phase arrays or other physical or chemical reactions such as manufacture of printed circuits, flat panel displays, semiconductor chips, nanotechnology, micro-electromechanical systems, flexible printed circuits, protein chips, lab-on-a-chip microfluidics and DNA chips.
In its broadest form the invention relates to the spatially defined deposition of any of a wide variety of chemical substances onto any predefined surface. Substances may include, but are not limited to, coloured materials, dyes, drugs, polymers, catalysts, anti-wetting agents, pigments, etching chemicals, conductors, metals such as gold, layerings and reagents for de-blocking, blocking, protecting and de-protecting, derivatisation and activation of solid phase chemical groups. Arrays can include pixel arrays for display panels, deoxyribonucleic acids (DNA), peptides, peptidenucleic acids (PNA), ribonucleic acids (RNA) and other solid phase chemical arrays and arrays assembled by combinatorial chemistry.
One form of the invention will be generally discussed in relation to manufacture of DNA arrays of the type generally known as DNA chips on substrates particularly planar substrates but the invention is not limited to that particular application but has wider ramifications and the invention is not intended to be limited to the manufacture of such DNA chips.
DNA chips (microarrays) are postage-stamp sized surfaces on which short segments of thousands of gene fragments (as single stranded DNA) are immobilized, of known sequence and in known locations. Because they are used to test for the presence of messenger RNAs and in tissue samples and/or for the level of expression of particular genes, these tethered DNA sequences (oligodeoxynucleotides) are called “probes”.
In one form of use, to profile tissue samples from malignant tumours, scientists extract messenger molecules (mRNA) involved in implementing genetic instructions within the tumours, make DNA or RNA copies, termed targets, often with amplification, eg polymerase chain reaction (PCR), label these with fluorescent markers, and flood these targets across the DNA chip. DNA probes on the chip will hybridise to the labelled targets and fluoresce if the patient's tumour extract contains one or more fluorescently labelled molecules (genetic instructions) that match one or more of the probe sequences and hybridises to it.
The molecules that bind to probes are called “targets”. Tissue samples containing a specific gene that is being more actively expressed with respect to a control, give rise to a probe cell that fluoresces more intensely when bound on the DNA chip than samples with little or no expression of that gene. The procedure is repeated with normal or reference tissue, and a computer then analyses the level of fluorescence to prepare a visual image comparing patterns of genetic activity in, for example malignant and normal tissue. In this manner it is possible to identify specific genes which are or may be involved in the malignancy, since specific zones, termed features of fluorescence can be related back to the segments (probes) of particular genes tethered in known locations on the DNA chip.
Selective de-protecting by direct light-activated chemistry or photo-removable de-protecting techniques has been developed but these are somewhat inefficient resulting in short impure solid phase oligodeoxynucleotides in rather large unit feature sizes of 10 to 50 microns. The applicant has surprisingly found that by the use of the present invention compositions which include the chemical de-protecting agent and which are selectively deposited on predefined areas of a planar or other shaped substrate under the influence of an electric field, then more accurate, localised and efficient de-protection may be possible. It is an object of this invention to provide a more efficient chemical de-protecting process.
Another form of the invention will be discussed with respect to manufacture of flat panel displays. In this form the invention relates to methods of making display devices using light emitting diodes (LEDs) such as polymer or organic light emitting diodes (OLEDs) as active layers. The method involves the direct deposition of LEDs or filters for LEDs such as patterned luminescent doped polymers and the fabrication of OLEDs and other semiconductor devices from these organic films.
There is increased interest in light emitting diodes made from organic polymers because of their potential low cost and potential applicability to colour flat panel displays. The organic materials are typically deposited by spin-coating (in the case of polymer materials), or by evaporation (in the case of small organic molecules). In either case, the single material covers the substrate so that only devices of a single colour can generally be fabricated. The straightforward integration of multiple organic layers (for the fabrication of red, green, and blue emitters as pixels for colour displays) requires the patterning of the individual organic layers using masks and screens. Because of their solubility in and sensitivity to aqueous solutions and many solvents, such patterning of organic materials by conventional photoresist and wet processing techniques is difficult. Efforts to date to integrate organic light emitting diodes with materials which emit different colours on the same substrate such as through the use of cathodes vapour-deposited through a shadow mask, such as dry-etch masks, have not been fully successful particularly for high resolution screens.
Different colours can be obtained in light emitting diodes by placing red, green and blue filter materials onto white LEDs or by placing red, green and blue emitting materials in proximity to each other using photoresist patterning and etching techniques to transfer the photoresist pattern into the polymer, however, such photoresist techniques are inapplicable to organic materials because the chemicals used for the photoresist process are incompatible with organic materials. Similarly, patterning subsequent layers on top of the organic materials (such as metal contacts) is difficult for the same reason. Vacuum deposited organic layers and metals may be patterned by vapour-depositing them through shadow masks, but this technology is difficult to extend to large areas and small pixel sizes with consequent registration problems.
An attractive feature of polymer or organic light emitting diodes is their very simple architecture. A basic device consists of an anode which is preferably indium tin oxide on a glass or plastic substrate, two thin polymer layers are then used, one of which is a polymer hole conducting layer (which can be a film of polyethylene dioxythiophene polystyrene sulphonate (PEDT/PSS) and the other of which is a conjugated polymer emissive layer. Then on the back a reflective cathode is provided. The whole device is then encapsulated to prevent the ingress of water. This invention in one form relates to the deposition in particular of one or more of these thin polymer layers.
There has been proposed the use of ink jet technology for the deposition of the polymer layers for OLEDs or the dyes for the polymers for OLEDs but there can be problems with this method of manufacture. This technology has problems with variable droplet size, satellite droplets, processing time, registration, droplet bounce and delivery restrictions. The viscosity of the OLED polymer “ink” is also limiting for the deposition of polymers.
Light emitting diode arrays may be passive or active matrix arrays. Passive arrays are powered directly by conductor arrays and active matrix arrays include single or poly-transistor switching to provide more even activation of the LEDs. This system uses switching conductor arrays and separate power supply for the LEDs. The method according to this invention may be applicable to either type of LED array but is particularly applicable to active matrix arrays.
It is an object of this invention to provide an alternative method of manufacture of multi-colour light emitting diode or light emitting polymer arrays for flat panel displays.
It is another object of the invention to provide a method for the spatially defined deposition of any of a wide variety of chemical substances onto any predefined surface.